1. Field of the Invention
The present invention relates to an electric power steering system.
2. Related Background Art
An electric power steering system for a vehicle is known in which the torque output from an electric motor for generating assist steering effort is reduced by a gear box in order to transmit proper torque and velocity to the output shaft of the steering system (see, for example, Japanese Utility Model Appln. Laid-Open No. 3-128565).
The electric power steering system disclosed in the above-mentioned reference has a housing whose bored cavity is formed by working one side of the housing so that two rolling bearings can be arranged in said bored cavity with high concentricity.
In the above-mentioned conventional electric power steering system, the end portions of the output shaft are supported by ball bearings. So, not only the housing should have a space for the ball bearing which is arranged near the electric motor, but also the output shaft should be considerably long. As a result, this type of electric power steering system cannot be mounted on a car which cannot afford sufficient space. In order to solve this problem, the diameter of the output shaft, and accordingly the dimensions of the steering system may be reduced by employing a needle bearing or a slide bearing instead of the ball bearing which is arranged at the innermost recess of the bored cavity of the housing. In this case, however, countermeasures should be necessary against the vibration and/or the noise generated by the output shaft which plays in its axial direction.